1. Field of the Invention
The present invention relates to a new class of precision flat and precision thickness abrasive media, processes for using the abrasive media, and apparatus for practicing processes with the abrasive media. The media are thin flexible abrasive sheeting used for grinding, flat lapping, polishing, finishing or smoothing of workpiece surfaces. In particular, the present invention relates to such processes and apparatus that use removable or replaceable sheeting having abrasive particle or abrasive agglomerate coated raised islands formed in annular bands that are able to operate at high surface speeds, and apparatus that secures the abrasive sheeting to a supporting platen. The support may optionally move the sheeting at those high speeds (preferably without the use of adhesive layers between the sheeting and the support). The apparatus, processes and abrasive media provide a high degree of control over the contact area or contact plane of the abrasive sheeting and the article that is to be lapped, polished, finished or smoothed. Uniform wear of the abrasive is experienced across the full annular band of abrasive material that allows a continuously flat abrasive surface to be presented to a workpiece. Also, the disks having narrow annular band of abrasive reduces areas of uneven wear material removal rates compared to conventional disks. Abrasive articles including sheets, long strips, and circular disks without annular bands all can have abrasive particle coated raised island structures that are attached to flexible backing materials can all be manufactured with abrasive island surfaces that are located in a common plane that is precisely parallel to the back mounting surface of the backing sheet. All of these abrasive articles having thin coatings of abrasive particles or abrasive agglomerates can be used at high and slow abrading surface speeds where all or most of the abrasive particles are utilized in grinding or lapping flat workpiece surfaces. Hydroplaning of the workpiece does not occur as a large proportion of the abrasive coolant water can pass between the raised island structures. The precision thickness control of the backing sheet abrasive articles assures that all of the abrasive material contacts a flat workpiece.
2. Background of the Invention
High speed lapping and grinding using fixed abrasive on sheet disks for both rough grinding and smooth polishing is now a practical reality. Most performance issues relate to two primary concerns, 1) hydroplaning caused by water lubricant and 2) vibrations created by grinding machine component dimensional inaccuracies and thickness variations of abrasive disks along their tangential surfaces. Unique answers for the first problem of hydroplaning have been defined, numerous solutions have been created and most of these solutions have been implemented or evaluated.
High quality abrasive article sheets that have certain important characteristics that are necessary for high speed flat lapping are not presently available in the marketplace. The sheets should be of a sufficient dimension (e.g., at least a 6 inch (15.2 cm) diameter, at least a 12 inch (30.5 cm) diameter, or at least an 18 inch (45.7 cm) or larger diameter, and have islands comprising abrasive structures (preferably secured to a substrate and preferably arranged in an annular band). The structures have an uppermost abrasive surface that is extremely flat and of uniform thickness. Conventional flat surface grinding or lapping platens are set up to use the full surface area of a circular shaped flat flexible sheet of abrasive. However, the abrasive contact surface speed of the rotating disk varies from a maximum speed at the outer radius to zero at the innermost center at the disk (where the radius is zero). The grinding material removal rate is roughly proportional to the surface speed of the moving abrasive, so that most of the grinding or lapping action, and the most efficient grinding or lapping action occurs at the outer portion of a rotating disk. Not only is the inside portion of the abrasive disk not used to remove workpiece surface material, but also this portion of the abrasive is not worn down by the workpiece, resulting in a shallow, cone shape of the abrasive disk surface. This uneven wear continues with usage of the disk, with the cone angle progressively increasing to a sharper angle. This cone angle is translated to the surface of the workpiece that is intended for rigid axis lapping of a workpiece and prevents precision flatness grinding of the workpiece, transferring uneven surface contour to the workpiece surface. An effective answer to this uneven wear is to create an abrasive disk with a narrow annular band of abrasive material (at the outer edges of the annulus), allowing the abrasive to wear down more evenly across the full surface of the abrasive disk (which is essentially the annulus, not a continuous circular surface) as the disk is used. This type of media is not available commercially and probably would not be with present production methods. This is because the continuous method of manufacturing abrasive disks cannot technically or economically produce the necessary annular configuration. Presently, an important method of manufacturing a circular abrasive sheets is to coat a continuous web backing with diamond particles or abrasive agglomerates to form a coated sheet material and then to punch out round disks from the coated sheet material. Effectively, most of the expensive inner surface area of these disks is wasted. If a conventional coated disk is used with a platen having an outer raised annular ring, then all of the abrasive coated area located at a radius inside the ring is not used as it does not contact the workpiece surface.
Furthermore, it is not practical to punch out radial rings from a coated web sheet for a number of reasons. First, there is not necessarily a ready market for the smaller disk that remains left over from the center punch-out for the annular ring. Also, there is a large waste of coated web material left over between the circular disks that are cut out, even with proficient “nesting” of the circular rings. Furthermore, the annular ring of coated abrasives made of thin 0.005 inch (0.127 mm) thick polyester web has limited structural body strength for handling and mounting so that it cannot be practically used on a platen without creating many problems, including the problem that water and grinding swarf tend to collect under the inside edge of the loose annular ring sheet. Furthermore, round or bar raised-abrasive islands having a thin top coating of expensive diamond particles are needed to compensate for hydroplaning affects at high surface speed lapping. The only island type of abrasive media now available which can reduce hydroplaning is a diamond particle metal plated Flexible Diamond Products abrasive sheet supplied by the 3M Company (Minnesota Mining and Manufacturing Co.). Disk shapes of this abrasive media is created by cutting circular shapes from a rectangular sheet of this material. However, due to the manufacturing process of this product, the product is commercially limited by at least two counts. First, each disk has large variations in flatness, or thickness, and, due to its unique construction, cannot be made flat enough to use effectively at high speeds where the unevenness is accentuated by the speed. Second, the Flexible Diamond Product abrasive sheet is constructed from plated diamonds which have been unable to produce a smooth polished finish.
Another widely used product from 3M Company is the pyramid shaped Trizact® abrasive which helps with hydroplaning effects. However, it is only practical for this product to be created with inexpensive abrasive media such as aluminum oxide which tends to wear fast and unevenly across its surface. Again, this is a continuous web type of product which does to have the capability of having precise thickness control.
Two common types of abrasive articles that have been utilized in polishing operations include bonded abrasives and coated abrasives. Bonded abrasives are formed by bonding abrasive particles together, typically by a molding process, to form a rigid abrasive article. Coated abrasives have a plurality of abrasive particles or abrasive agglomerates bonded to a backing by means of one or more binders. Coated abrasives utilized in polishing processes are typically in the form of endless belts, tapes, or rolls which are provided in the form of a cassette. Examples of commercially available polishing products include “IMPERIAL” Microfinishing Film (hereinafter IMFF) and “IMPERIAL” Diamond Lapping Film (hereinafter IDLF), both of which are commercially available from Minnesota Mining and Manufacturing Company (3M Company), St. Paul, Minn.
Structured abrasive articles have been developed for common abrasive applications. Pieper et al., U.S. Pat. No. 5,152,917 discloses a structured abrasive article containing precisely shaped abrasive composites. These abrasive composites comprise a plurality of abrasive grains and a binder. Mucci, U.S. Pat. No. 5,107,626, discloses a method of introducing a pattern into a surface of a workpiece using a structured abrasive article.
A new class of large diameter precise thickness disks which have an annular ring of raised islands coated with a thin coat of diamond abrasive particles or abrasive agglomerates is required for high speed lapping which requires a completely different manufacturing technique than has been employed in the past by the abrasives industry. The new batch type of processing required to produce these disks must be practical and cost effective. Eventually, this batch process of manufacturing a abrasive disk as a separate item can be converted partially or wholly into a continuous web-line process when the product sales volume demand warrants the investment in the required process equipment and converting technology. The abrasive agglomerates used include spherical shaped beads that have small diamond or other abrasive particles enclosed in a friable ceramic or metal oxide matrix where the ceramic erodes as the bead is abrasively worn down thereby progressively exposing new sharp abrasive particles. Abrasive agglomerates may also have many shapes other than spherical.
The primary competitor for the sheet fixed abrasive polishing technology is slurry lapping, which is necessarily very slow, even though it has been progressively up-dated. Slurry lapping produces a flatter surface on a workpiece at the present time than can be accomplished by high speed lapping, which has limited the sale of the high speed lapper machines. Other traditional grinding wheel machines can produce about the same flatness accuracy as the present configuration lapper but these machines can not produce the associated smooth polish that typical precision workpiece parts require. Accurate flat and smooth workpiece part surfaces are used to prevent leakage when these parts are mated stationary with other moving parts or when the workpiece parts are joined to dynamically rotate against each other.
High speed lapping uses expensive thin flexible abrasive coated disks that must be very precise in thickness and must also be attached to a platen that is very flat and stable. As the platen rotates very fast, this speed tends to “level” the abrasive as it is presented to the workpiece surface. As only the high spots of the abrasive contact the workpiece, the remainder of the disk abrasive is not used until the high spots wear down. Thus, it is necessary for the total system to be precisely aligned and constructed of precision components to initialize the grinding. Furthermore, the wear of the abrasive must proceed uniformly across both the surface of the sheet and the surface of each island to maintain the required flatness of both the effective abrasive surface and correspondingly, the workpiece surface. These issues have all been addressed here in defining various configurations of high speed lapper machines along with different abrading process techniques employed in operating the machines. To generate even workpiece surface wear with rotating abrasive disks, an annular raised abrasive flat surface is used as taught by Duescher in U.S. Pat. Nos. 6,149,506, 6,120,352; 6,102,777; 6,048,254; 5,993,298; 5,967,882; and 5,910,041 which are incorporated herein by reference. However, the desired large diameter flexible backing disks which are required for abrading large workpiece parts are not available as the size of commercially available abrasive disks is presently limited to about 12 inches (30.5 cm) diameter. This relatively small disk size severely limits the width of the annular abrasive band (or ring). A wide abrasive band on a small diameter disk results in a much slower surface grinding speed at the inside diameter of the band than the surface speed at the outside diameter of the band. This slower surface speed also results in reduced material removal from the portion of the workpiece that is located at this inside radial location. Furthermore, as the inside radial section of the abrasive disk wears slowly, the outside diameter portion of the abrasive progressively wears down much faster which results in an uneven abrasive surface across the surface of the annular band. Having larger nominal diameter abrasive disks with narrow annular bands, relative to the disk diameter, will inherently take care of most of these problems. A large diameter disk can have a wide annular band, where the annular width is measured in a radial direction, and the variation of the abrading surface speed across the radial width of the abrasive band will be minimized. The surface speed of an annular band will vary in direct proportion to the radial location of the abrasive. If a large nominal annular band diameter is used and the abrasive band width is narrow, the radius of the extreme inner radius of the band and the radius of the extreme outer radius of the annular band will be close in value. Because the radii of the inner and outer edges of the annular band are close in value, the abrading surface speed of the whole abrasive area will be fairly uniform. The larger the inner and outer annular band radii change in proportion to each other, the larger the variation the surface speed will occur across the radial width of the annular band width.
The typical workpieces that are lapped initially are not flat and have rough surfaces. Most potential customers seem to want both very flat (within 2 Helium light bands or 22.3 microinches or 0.6 micrometers) and smooth polished surfaces.
A preferred abrasive flat lapping process is now done in two separate steps. First, the parts are ground flat using a rigid spindle running at full 3,000 RPM speed, a very small contact force of 1 to 2 lbs. (0.454 to 0.908 kg) and typically, 3M Company's metal plated diamond abrasive. Water flows between the round islands of abrasive, reducing hydroplaning. Hydroplaning typically produces a cone shaped ground surface. Second, parts are polished using a spherical action workpiece holder, with low to moderate contact forces of 2 to 15 lbs. (0.908 to 6.81 kg), and uses a smooth coated abrasive disk operating at lower speeds of about 1,000 RPM or less to prevent hydroplaning. At this time, no “island type” of coated abrasive is available for polishing in combination with an effective polishing method.
Generally, use of the metal plated diamond island style abrasive disks to remove material is consider to be “grinding,” as the surface finish is not smooth to the high standards of polishing that is required for flat lapping. Use of the coated (non plated) flat-surface flexible sheet abrasive articles can create very smooth surfaces and their use is considered to be “lapping”. The plated diamond island disks tend to be very durable and may last a long time during abrading use. The coated diamond and other abrasive particle disks are much more fragile and are consumed much more rapidly.
With respect to performance, with rigid flat grinding, 2 Helium light bands (or 22.3 microinches or 0.6 micrometers) of flatness are obtained which is too high for most applications. Polishing results in acceptable smoothness but typically creates new problems with flatness because of hydroplaning. Flatness defects created in the polishing step are both cone shapes and saddle shapes.
The high surface speed of the plated island abrasive creates extraordinary high rates of material removal of very hard materials and this perhaps can be increased even further with higher speeds. This is the primary reason for the interest of the high speed grinding and lapping. There probably is a significant business just in the use of this grinding portion of the process to initially prepare parts for the subsequent smooth lapping processing by other traditional methods such as slurry lapping to finish the parts. However, this initial “fast grind” does not appear to be of sufficient benefit to introduce this totally new technology to the marketplace.
Hydroplaning of parts using fine small particle coated abrasive will always be a problem at very high speeds until an abrasive article disk is available which has “islands” of abrasive which allows excess water to pass around the island edges. A recent new commercial form of abrasive disks which has the abrasive formed into small pyramids of abrasive is available and it works well from a hydroplaning standpoint when the pyramids are fresh and not worn down. However, this Trizact brand disk sold by 3M Company is created only with relatively soft aluminum oxide and tends to wear out fast. It is not logical that the manufacturer would use longer wearing diamond particles in these pyramid shapes as each disk would consume so much diamond that the costs would be too high.
U.S. Pat. No. 5,611,825 (Engen) describes resin adhesive binder systems which can be used for bonding abrasive particles to web backing material, particularly urea-aldehyde binders. There is no reference made to forming or abrasive coating abrasive islands. He describes the use of make, size and super size coatings, different backing materials, the use of methyl ethyl ketone and other solvents. Loose abrasive particles are either adhered to uncured make coat binders which have been coated on a backing or abrasive particles are dispersed in a 70 percent solids resin binder and this abrasive composite is bonded to the backing. Backing materials include very flat and smooth polyester film for common use in fine grade abrasives which allow all the particles to be in one plane. Primer coatings are used on the smooth backing films to increase adhesion of the make coating. Water solvents are desired but organic solvents are necessary for resins. Fillers include calcium metasilicate, aluminum sulfate, alumina trihydrate, cryolite, magnesia, kaolin, quartz, and glass. Grinding aid fillers include cryolite, potassium fluroborate, feldspar and sulfur. Backing films include polyesters, polyolefins, polyamides, polyvinyl chloride, polyacrylates, polyacrylonitrile, polystyrene, polysulfones, polyimides, polycarbonates, cellulose acetates, polydimethyl silotanes, polyfluorocarbons. Priming of the backing to improve make coating adhesion includes a chemical primer or surface alterations such a corona treatment, UV treatment, electron beam treatment, flame treatment and scuffing. Solvents include acetone, methyl ethyl ketone, methyl t-butyl ether, ethyl acetate, acetonitrile, tetrahydrofuran and others such as methanol, ethanol, propanol, isopropanol, 2-ethoxyethanol and 2-propoxyethanol. Abrasive filled slurry is coated by a variety of methods including knife coating, roll coating, spray coating, rotogravure coating, and like methods. Resins used include resole and novolac phenolic resins, aminoplast resins, melamine resins, epoxy resins, polyurethane resins, isocyanurate resins, urea-formaldehyde resins, isocyanurate resins and radiation-curable resins. Different examples of make, size and supersize coatings and their quantitative amounts of components were given.
U.S. Pat. No. 4,903,440 (Kirk) describes the use of different reduced-cost drum cured binder abrasive particle adhesives which allow elimination of the use of web festoon ovens which are used because of the long cure times required by conventional phenolic adhesives used for abrasive webs. Typically a pre-coat, a make coat, having loose abrasive particles imbedded into the make coat and then a size coat are applied to a continues web backing. No reference is given to processing individual abrasive articles such as abrasive disks. Rather, a continuous backing web is coated with binders and abrasive particles, the binders are cured and then the web is converted into abrasive products such as disks or belts. Resole phenolic resins which are somewhat sensitive to water lubricants are catalyzed by alkaline catalysts and novolac phenolic resins having a source of formaldehyde to effect the cure are described. Viscosity of some binders are reduced by solvents. Fillers include calcium carbonate, calcium oxide, calcium metasilicate, aluminum sulfate, alumina trihydrate, cryolite, magnesia, kaolin, quartz and glass. Grinding aid fillers include cryolite, potassium fluroborate, feldspar and sulfur. Super size coats can use zinc stearate to prevent abrasive loading or grinding aids to enhance abrading. Coating techniques include two basic methods. The first is to provide a pre-size coat, a make coat, the initial anchoring of loose abrasive grain particles and a size coat for tenaciously holding abrasive grains to the backing. The second coating technique is to use a single-coat binder where a single-coat takes the place of the make coat/size coat combination. An ethyl cellosolve and water solvent is referenced for use with a resole phenolic resin.
U.S. Pat. No. 4,038,046 (Supkis) describes abrasive articles made with a blend of urea formaldehyde and alkaline catalyzed resole phenolic binder resins which are cured with the same curing time and temperatures as conventionally used for phenolic resins. Abrasive particles applied by gravity and also by electro-coating methods. A typical oven cure cycle of the web is 25 minutes at 125 degrees F., 25 minutes at 135 degrees F., 18 minutes at 180 degrees F., 25 minutes at 190 degrees F., 15 minutes at 225 degrees F. and 8 hours at 230 degrees F. Yellow and blue dyes are mixed in the binder system.
U.S. Pat. No. 4,710,406 (Fugier) describes a production method for the manufacture of a condensation reaction phenolic resin with different alkali catalysts and which can be diluted up to 1,000 percent.
U.S. Pat. No. 4,426,484 (Saeki) describes phenolic resins which have the cure time accelerated by using special additives.
U.S. Pat. No. 5,304,225 (Gardziella) describes phenolic resins which typically have high viscosity which can be lowered by the addition of solvents or oils.
U.S. Pat. No. 5,397,369 (Ohishi) describes phenolic resins used in abrasive production which have excessive viscosity where a large amount of solvent is required for dilution to adjust the viscosity within an appropriate range. Examples of organic solvents with high boiling points include cyclohexanone, and cyclohexanol. Solvents having an excessively high boiling point tend to remain in the adhesive binder and results in insufficient drying. When the boiling point of a solvent is too low, the solvent leaves the binder too fast and can result in defects in the abrasive coating, sometimes in the form of foamed areas. Additives such as calcium carbonate, silicone oxide, talc, etc. fillers, cryolite, potassium borofluoride, etc. grinding aids and pigment, dye, etc. colorants can be added to the second phenolic adhesive (size coat) used in the abrasive manufacture.
U.S. Pat. No. 5,674,122 (Krech) described screen abrasive articles where the abrasive particles are applied to a make coat of phenolic resin by known techniques of drop coating or electrostatic coating. The make coating is then at least partially cured and a phenolic size coating is applied over the abrasive particles and both the make coat and size coat are fully cured. Make and size coats are applied by known techniques such as roll coating, spray coating, curtain coating and the like. Optionally, a super size coat can be applied over the size coat with anti-loading additive of a stearate such as zinc stearate in a concentration of about 25 percent by weight optionally along with other additives such as cryolite or other grinding aids. In addition, the abrasive coating can be applied as a slurry where the abrasive particles are dispersed in a resinous binder precursor which is applied to the backing by roll coating, spray coating, knife coating and the like. Various types of abrasive particles of aluminum oxide, ceramic aluminum oxide, heat-treated aluminum oxide, white-fused aluminum oxide, silicone carbide, alumina zirconia, diamond, ceria, cubic boron nitride, garnet and combinations of these in particle sizes ranging from 4 to 1300 micrometers can be used.
U.S. Pat. No. 4,251,408 (Hesse) describes phenolic resins used in preparation of abrasives where rapid curing as a result of increasing the curing temperature tends to form blisters which impairs the adherence of the resin to the substrate backing. Special cure cycles are used which have low initial curing temperatures with regulated, progressively increasing temperature which prevent blister formation but the time required for cross-linking is thereby increased. Drying and curing of webs by use of loop dryers or festoon dryers are discussed which provide both the function of driving off the solvents from the binder and to cross-link cure the binder. The cure rate of a resin is defined by the B-time which is the time required to change from a liquid state to reach the rubbery elastomer state (B-state).
U.S. Pat. No. 5,551,961 (Engen) describes abrasive articles made with a phenolic resin applied as a make coat used to secure abrasive particles to the backing by applying the particles while the make coat is in an uncured state, and then, the make coat is pre-cured. A size coat is added. Alternatively, a dispersion of abrasive particles in a binder is coated on the backing. The use of solvents is described to reduce the viscosity of the high viscous resins where high viscosity binders cause “flooding”, i.e., excessive filling in between 30 to 50 micrometer abrasive grains. Also, non-homogenous binder resins result in visual defects and performance defects. Both flooding and non-homogenous problems can be reduced by the use of organic solvents which are minimized as much as possible. Resole phenolic resins experience condensation reactions where water is given off during cross linking when cured. These phenolics exhibit excellent toughness, dimensional stability, strength, hardness and heat resistance when cured. Fillers used include calcium sulfate, aluminum sulfate, aluminum trihydrate, cryolite, magnesium, kaolin, quartz and glass and grinding aid fillers include cryolite, potassium fluoroborate, feldspar and sulfur. Abrasive particles include fused alumina zirconia, diamond, silicone carbide, coated silicone carbide, alpha alumina-based ceramic and may be individual abrasive grains or agglomerates of individual abrasive grains. The abrasive grains may be orientated or can be applied to the backing without orientation. The preferred backing film for lapping coated abrasives is polymeric film such as polyester film and the film is primed with an ethylene acrylic acid copolymer to promote adhesion of the abrasive composite binder coating. Other backing materials include polyesters, polyolefins, polyamides, polyvinyl chloride, polyacrylates, polyacrylonitrile, polystyrene, polysulfones, polyimides, polycarbonates, cellulose acetates, polydimethyl siloxanes, polyfluocarbons, and blends of copolymers thereof, copolymers of ethylene and acrylic acid, copolymers of ethylene and vinyl acetate. Priming of the film includes surface alteration by a chemical primer, corona treatment, UV treatment, electron beam treatment, flame treatment and scuffing to increase the surface area. Solvents include those having a boiling point of 100 degrees C. or less such as acetone, methyl ethyl ketone, methyl t-butyl ether, ethyl acetate, acetonitrile, and one or more organic solvents having a boiling point of 125 degrees C. or less including methanol, ethanol, propanol, isopropanol, 2-ethoxyethanol and 2-propoxyethanol. Non-loading or load-resistant super size coatings can be used where “loading” is the term used in the abrasives industry to describe the filling of spaces between the abrasive particles with swarf (the material abraded from the workpiece) and the subsequent buildup of that material. Examples of load resistant materials include metal salts of fatty acids, urea-formaldehyde resins, waxes, mineral oils, cross linked siloxanes, cross linked silicones, fluorochemicals, and combinations thereof. Preferred load resistant super size coatings contain zinc stearate or calcium stearate in a cellulose binder. In one description, the make coat precursor can be partially cured before the abrasive grains are embedded into the make coat, after which a size coating precursor is applied. A friable fused aluminum oxide can be used as a filler.
U.S. Pat. No. 5,137,542 (Buchanan) describes a coated abrasive article which has a coated layer of conductive ink applied to the surface of the article, either as a continuous film or the back side of the backing or as printed “island” patterns on the abrasive particle size of the article to prevent the buildup of static electricity during use. Static shock can cause operator injury or ignite wood dust particles. The islands coated on 3M Company Imperial® abrasive were typically quite large 1 inch (2.54 cm) diameter dots and cover only about 22 percent of the article surface. Further, they are very thin, about 4 to 10 micrometers. No reference is made to the affect of the raised islands on hydroplaning effects when used with a water lubricant and no reference is made to high speed lapping. Raised islands of this height would provide little, if any, benefit for hydroplaning. Further, islands of this large diameter would also develop a significant boundary layer across its surface length. Also, top coatings such as these electrically conductive particle filled materials would not allow the typically small mono layers of diamonds used in lapping films to abrasively contact the workpiece surface until the static coating was worn away, after which time it is no longer effective in static charge build-up prevention. Description is made of using polyester film as a backing material for lapping abrasive articles. Bond systems include phenolic resins and solvents include 2-butoxyethanol, toluene, isopropanol, or n-propyl acetate. Coating methods include letterpress printing, lithographic printing, gravure printing and screen printing. For gravure printing, a master tool or roll is engraved with minute wells which are filled with coatable electrically conductive ink with the excess coating fluid removed by a doctor blade. This coating fluid is then transferred to the abrasive article.
U.S. Pat. No. 5,108,463 (Buchanan) describes carbon black aggregates incorporated into a super size coat which also included kaolin.
U.S. Pat. No. 5,221,291 (Imatani) describes the use of a polyimide resin for the combination use as an adhesive bonding agent for abrasive particles, and also, to form an abrasive sheet. Diamond particles were dispersed in solvent thinned polyimide resin and coated on a flat surface with 60 micrometer diamond particles. The sheet was tested at very low speeds of 60 rpm but did remove material, leaving a smooth workpiece surface even though the particles were principally buried within the thickness of the resin which also formed the thin abrasive disk sheet. Most of the expensive diamonds are lost for use as grinding agents but the polyimide successfully bond the diamonds within the sheet.
U.S. Pat. No. 5,368,618 (Masmar) describes preparing an abrasive article in which multiple layers of abrasive particles, or grains, are minimized. Some conventional articles have as many as seven layers of particles which is grossly excessive for lapping abrasive media. He describes “partially cured” resins in which the resin has begun to polymerize but which continues to be partially soluble in an appropriate solvent. Likewise, “fully cured” means the resin is polymerized in a solid state and is not soluble. If the viscosity of the make coat is too low, it wicks up by capillary action around and above the individual abrasive grains such that the grains are disposed below the surface of the make coat and no grains appear exposed. Phenolic resins are cured from 50 degrees to 150 degrees C. for 30 minutes to 12 hours. Fillers including cryolite, kaolin, quartz, and glass are used. Organic solvents are added to reduce viscosity. Typically 72 to 74 percent solids are used for resole phenolic resin binders. Special tests demonstrate that a partially cured resin is capable of attaching loose abrasive mineral grains which are drop coated onto test slides with the result that higher degree of cure results in lower mineral pickup and lower degree of cure results in less mineral pickup. Abrasive grains can be electrostatically projected into the make coat where the ends of each grain penetrates some distance into the depth of the make coat. No description was provided about the desirability, necessity, or ability of the grain application process having a flat uniform depth of the tops of each particle for high speed lapping.
U.S. Pat. No. 5,924,917 (Benedict) describes methods of making endless belts using an internal rotating driven system. He describes the problem of “edge shelling” which occurs on small width endless belts. This is the premature release of abrasive particles at the cut belt edge. He compensates for this by producing a belt edge that is very flexible and conformable. The analogy to this edge shelling occurs on circular abrasive disks also. To construct a belt, an abrasive web is first slit to the proper width by burst, or other, slitting techniques which tends to loosen the abrasive particles at the belt edge when the abrasive backing is separated at the appropriate width for a given belt. These edge particles may be weakly attached to the backing and they may also be changed in elevation so as to stick up higher than the remainder of the belt abrasive particles. Similarly, when a disk is punched out by die cutting techniques from a web section, the abrasive particles located on the outer peripheral cut edge are also weakened. This happens particularly for those discrete particles which were pushed laterally to the inside or outside of the die sizing hole by the matching die mandrel punch. Other types of cutting, slitting or punching abrasive articles from webs also create this shelling problem including water jet cutting, razor blade cutting, rotary knife slitting, and so on. Resole phenolic resins are alkaline catalyzed by catalysts such as sodium hydroxide, potassium hydroxide, organic amines or sodium carbonate and they are considered to be thermoset resins. Novolac phenolic resins are considered to be thermoplastic resins rather than thermoset resins which implies the novolac phenolics do not have the same high temperature service performance as the resole phenolics. Resole phenolic resins are the preferred resins because of their heat tolerance, relatively low moisture sensitivity, high hardness and low cost. During the coating process, make coat binder precursors are not solvent dried or polymerized cured to such a degree that it will not hold the abrasive particles. Generally, the make coat is not fully cured until the application of the size coat which saves a process step by fully curing both at the same time. Fillers include hollow or solid glass and phenolic spheroids and anti-static agents including graphite fibers, carbon black, metal oxides, such as vanadium oxide, conductive polymers, and humectants are used. Abrasive material encompasses abrasive particles, agglomerates and multi-grain abrasive granules. Belts are produced by this method using a batch process. The thermosetting binder resin dries, by the release of solvents, and in some instances, partially solidified or cured before the abrasive particles are applied. The resin viscosity may be adjusted by controlling the amount of solvent (the percent solids of the resin) and/or the chemistry of the starting resin. Heat may also be applied to lower the resin viscosity, and may additionally be applied during the processes to effect better wetting of the binder precursor. However, the amount of heat should be controlled such that there is not premature solidification of the binder precursor. There must be enough binder resin present to completely wet the surface of the particles to provide an anchoring mechanism for the abrasive particles. A film backing material used is PET, polyethylene terephthalate having a thickness of 0.005 inch (0.128 mm). Solvents used include trade designated aromatic 100 and Shell® CYCLO SO 53 solvent.
U.S. Pat. No. 5,318,604 (Gorsuch et al.) and 4,863,573 (Moore et al.) describes abrasive articles made by metal plating islands of which are top coated with diamond abrasives that have been plated onto the islands. The technique employed is to create an island by printing an insulation solder photo resist insulation pattern over an electrical conducting plate and overlaying this with a woven non-electrical conduction cloth mesh. When immersed in a plating bath, a metal plated island is formed integral with the cloth mesh over the electrically exposed island areas of the photo resist covered metal conducting plate. After a minimum height of metal plated island area is built up by metal progressively covering the island area of interlocking mesh fiber strands, diamond particles are suspended in the plating bath liquid and allowed to free fall by gravity onto the mesh. Those particles that fall into the small island areas, which are very irregular in shape due to the unevenness of the interlocking fibers, are progressively plated onto the existing metal plated surfaces. However, the individual plated abrasive particles do not lie in a common flat plane. Instead, the particles are electroplate bonded on the curved surface of the raised islands, and also, are attached at many different random elevations within the upper portion of island structures. This abrasive particle out-of-flatness condition, where each particle is at a different elevation, occurs in part, because of uneven metal deposition rates that occur over the surface of the drum at all the different island locations during the process of building-up the height of each island. Also, a random uneven particle deposition occurs over time when particles come out of solution and are deposited in the final portion of the island build-up. The presentation of the individual particles to the raised island area is completely random. Some particles will fall deep into the “log pile” mesh, and others will land on the top curved surface of an individual cylindrical mesh fiber. Some of the abrasive particles will come to rest on other particles that have already been plated onto the mesh, forming standing “rock towers” of particles. Further, the plating process creates nominal island height differences that vary from island to island, in part, due to the different characteristics of the individual fibers of the mesh cloth. The height thickness of each island, as measured from the surface of the plated abrasive particles to the backside of the mesh cloth, or to the island bottom, is not precisely uniform. Another thickness tolerance disadvantage of this product occurs when the plated cloth material is stripped from the electrically conductive metal base and attached with adhesive to a backing substrate sheet to form a laminated abrasive article. This laminated abrasive article does not have precise overall thickness control due to thickness variations in the island plated cloth material, in the backing sheet, and due to thickness variations in the laminating adhesive layer. There is no possible height control mechanism that can be employed to assure that there exists a uniform flat level surface of the individual diamond abrasive particles over the complete surface area of the abrasive article. Diamonds that are bonded at different elevations below the uppermost surface of the top surface of the fiber “logs” in the “log jam” that forms the foundation of the raised island structures are not used and are wasted. Further, there is no control over the thickness variation of the woven mesh material and no description of techniques to level-smooth it down to the surface of the photo resist covered electrical conducting plate used as a geometric reference base for the plating process. After sufficient plating has been achieved, the electrically insulated cloth, made of plastic fibers, is stripped away from the photoresist plate, which can be used again with another mesh cloth. The cloth can then be attached to a backing material or it can be dissolved away with strong chemicals or acids. Attaching the plated cloth with PSA (pressure sensitive adhesive) to a backing introduces new variance in the total thickness of the abrasive article. This process can be used to produce a rectangular sheet, but when a circular disk is punched out with the use of a punch-and-die set, the round surface of the die set will intersect with small portions of the typical round islands and either remove a sliver from some islands, or, leave just a sliver of a rather tall island weakly attached to the backing. In either case, the shearing action of a die punch will tend to jam the sliver portion of the island into the matching die set members. This jamming action will introduce unbalanced forces that will tend to push the island, or a crescent shaped sliver of an island sideways, which will weaken the islands structural attachment to the disk backing. Then the problem of “edge shelling” described earlier occurs and these raised island edge-slivers, or whole island structures, will tend to break loose during grinding and cause scratches that will occur on a lapped workpiece surface. Flex-Diamond® electroplated type of raised island diamond abrasive article sheets available from the 3M Company, St Paul, Minn. have been used to flat-grind workpiece surfaces at high rotational surface speeds using 12 inch (30.5 cm) diameter abrasive disks and these disks have successfully produced workpiece surfaces that had a very precise flatness. There was no indication of the occurrence of hydroplaning of the workpiece using the electroplated raised island product at rotational speed of up to 3,000 RPM. However, these precisely flat workpiece surfaces were simultaneously not polished smooth by the rotating disk abrading action, where the smoothness is relative to the micron size rating of the abrasive particle size of the abrasive article. Flat surfaced (non-island) abrasive disk articles of the same 12 inch (30.5 cm) diameter size having the same abrasive particle size rating tended to produce polished workpiece surface that were much smoother than was produced by the electroplated raised island articles under the same rotational speed conditions but these smooth surfaces were not precisely flat. This plated raised island product cannot be used to produce a precisely smooth and flat workpiece surface, primarily because of the non-uniformity of the elevation of individual abrasive particles that are electroplate bonded to the irregular shaped raised island structures. The mesh plastic cloth is used to produce the abrasive coated islands as it can be easily stripped away from the photo resist plate. Direct plating of abrasive particles to the top surface of island structures is described by Gorsuch but is not used as it is too difficult to separate the direct plated island from the electrically exposed areas of the photo resist plate. There is no discussion of the concerns of hydroplaning of the workpiece when used at the high speeds desired for abrading with diamond abrasive which the height of the raised islands easily prevents. Instead, there is only discussion of a passageway for the water to travel outward to flush out the swarf generated as grinding particles are removed from the workpiece surface. Gorsuch makes an attempt to produce a flat level diamond abrasive surface, indicating he is aware of only the fundamental problem with this invention. He first plates a thin layer of metal in an array of islands “upside down” on a smooth cylinder. Then he plates on a layer of diamonds, which is followed by adding a cloth mesh and then adds a layer of metal plating on top of the diamonds which are now fully encapsulated into the thick layer of plated metal. The mesh is stripped off the drum to use the diamonds that originally lay on the flat surface of the drum. However, all the diamonds are completely buried in the plated metal and are useless for use as an abrasive article. Further, there was no description of uncurling a sheet of this material from the curvature of the drum and laying it flat for use as a disk without bending or distorting the abrasive metal plated sheet. The top surface of the raised island is formed in a non-flat cylindrical shape that matches the cylindrical curvature of the surface of the plating drum. Another part of the invention produces a disk with islands of abrasive. These are very thick disks that have a pattern of islands which are raised 25 percent to 50 percent (of the overall thickness of the disk) above the disk base or backing. A thick layer of abrasive slurry of abrasive particles mixed in a resin is deposited on a backing and the thickness is controlled by the use of mold plates. No description is made of how critical it is to control the flatness of the upper surface of the molded layer of abrasive, or of how the abrasive surface is maintained flat during wear. Further, no description was made of any of the issues of hydroplaning at high speed with water lubricants which is a primary concern for use with high speed lapping. A description is given of the use of very large hemispherical elements of metal that have a diameter of 0.5 to 3 mm which has generally only five abrasive particles which have a very large average size of 250 micrometer diameter. These abrasive particles are located at the top and along the lower side walls of each hemisphere and are metal plated to be embedded from 30 percent to 50 percent as an integral part of the metal hemisphere. These hemispheres are high enough to act as islands and the rounded tops would also aid in preventing hydroplaning at high speeds. However, this type of construction with very tall domes having only a single abrasive particle located on the very apex of the dome peak has little use for lapping. The single particle will be very aggressive in material removal but it will only produce distinct scratches as it removes a single track of material as it passes over a workpiece surface. This highest particle will have to become worn down along with some of the parent metal used for the dome construction before another particle will be active in partnership with the first. Having only five particles on a huge dome means most of the whole dome must effectively be worn down before the lower particles are engaged as grinding elements. The whole abrasive grinding load forces are so concentrated on single grains of abrasive that the grains tend to be knocked out of place, or “pulled” from the very strong plated metal binding. Use of expensive abrasive particles such as diamond seems totally out of place economically for this type of abrasive article construction. It has absolutely no value for lapping. None of the plating methods employed in this plating technique of forming abrasive articles has any capability of controlling the height of the particles relative to the backside of a backing, which is a critical factor for lapping at high surface speeds.
U.S. Pat. No. 4,256,467 (Gorsuch) describes an abrasive article with diamond particles plated onto an electrically insulated mesh cloth which can be cut into a “daisy wheel” for use in grinding curved, convex, or concave optical lenses. These articles are intended for rough grinding and not for lapping. A electrically conductive smooth metal cylindrical drum is coated with an insulating resist except in circular dot or spot areas where metal plating is desired. An electrically insulating woven cloth, typically made of common plastic fiber materials, is stretched over the whole drum surface including both the conductive spot areas and the resin insulated drum areas. The cloth covered drum is then placed in a plating tank and electroplating then starts where metal is plated through the cloth at the conductive spot areas. Buildup of plated metal occurs at the circular spots and electroplating continues until the desired plated metal thickness is reached to form raised islands that extend through the cloth thickness and above the curved cylindrical drum surface. Then small diamond particles are introduced into the electroplating bath liquid and plating continues, thereby trapping some of these diamond particles at the island top surface by metal electroplate bonding them to the exposed surface of the previously plated island areas. The plating action is stopped, the drum is removed from the bath and the cloth is separated from the drum surface to provide a cloth material having integral raised islands that have non-flat drum-cylinder shaped curved top surfaces that are covered with abrasive particles. The drum is described as being optionally rotated. After plating these diamond particles on the island top surfaces, the particles will all have different heights relative to the drum surface, and thus, relative to the bottom of the cloth due to a number of factors. It is well known that metal plating varies in thickness over different areas of a plated member simply due to variables inherent in an electro-plating process. Also, the woven cloth will have different thicknesses due to variations in the weaving machine performance. Also, there are variances in the thickness of individual woven cloth strands of the very fine denier fibers that are joined together to form a single strand. Further, the sleeve of material is stretched and pulled over the cylindrical drum, which can cause variations in the cloth thickness around the surface of the drum. All of these factors result in a flexible abrasive that can be cut into weak strips or legs that are fanned out from a common hub to form a daisy wheel article where the legs will conform to a curved lens when used at very low speeds. The individual stiff metal raised abrasive island structure surfaces of this daisy wheel will not locally conform, across the semi-rigid surface area of a typical metal plated flat abrasive island, to a curved lens surface. In fact, as the individual raised islands have the same curved surface shape as the drum surface, these island shapes will not lay in flat contact with a flat workpiece surface and also will not lay in conformance to a spherical lens curvature. Use of these stiff metal abrasive islands in abrading contact with the curved lens surface can result in abrading contact to be concentrated at a very small portion of a raised island structure. A plated metal portion of the island structure may contact the curved lens at a raised island location that does not contain abrasive particles, or it is possible that a single abrasive particle that is plated at the highest elevation of that portion of the raised island structure will alone contact the curved portion of the lens which will result in undesirable scratches of the lens surface by that single particle. This daisy wheel article is not useful for high speed lapping which requires extremely precise abrasive article thickness control. Again, in this patent, as was the case in his U.S. Pat. No. 5,318,604, he acknowledges and addresses the issue of obtaining an abrasive article that does, in fact, have all the abrasive particles in the same plane. This is done producing a cloth mesh island abrasive covered article with use of plastic cloth over a patterned drum. Here, he electroplates islands of metal over exposed areas and electroplates particles dropping out of the plating solution to these plated islands after which he continues to build up the metal plating thickness, add a cloth, continue plating, and then remove the cloth mesh from the drum. The islands are refereed to as having flat plane abrasive surfaces but island flat plane surface can not be produced from a cylindrical drum surface. The resultant article would seem to have little use as a abrasive article as the diamond particles are not exposed at the drum surface, but rather, are enclosed or buried within the plated metal layer by the progressively built-up plating metal. As they are not exposed from the plated metal surface, they cannot effect their abrasive cutting action. Also, the backside thickness of plated metal would vary in height due to variances in the deposition rate of material over each island site to variances in electrical conductivity of the unknown coating applied over each site which allows the plated metal to be peeled from the drum. When the cloth is turned over, and mounted to a backing, the variance in height of each island, as measured from the front surface of the diamonds to the cloth bonded surface of the backing, will be significant over the whole surface of the abrasive article. This abrasive article would have no use for high speed lapping where the high speed of a rotating platen establishes an abrasive sheet mounting flatness plane more precise as the platen rotation speed is increased. The requirements of high speed lapping far exceed the capability of this system of creating abrasive articles.
U.S. Pat. No. 5,549,962 (Holms) describes the use of pyramid shaped abrasive particles by use of a production tool having three-dimensional pyramid shapes generated over its surface which are filled with abrasive particles mixed in a binder. This abrasive slurry is introduced into the pyramid cavity wells and partially cured within the cavity to sufficiently take on the shape of the cavity geometry. Then the pyramids are either removed from the rotating drum production tool for subsequent coating on a backing to produce abrasive articles, or, a web backing is brought into running contact with the drum to attach the pyramids directly to the backing to form an abrasive web article. If a web backing is used is contact with the drum, the apexes of the pyramids are directed away from the backing. If loose discrete pyramids are produced by the drum system, the pyramids can be oriented on a backing with the possibility of having the pyramid apex up, or down or sideways relative to the backing. The pyramid wells may be incorporated into a belt and also, these forms can extend through the thickness of the belt to aid in separating the abrasive pyramid particles from the belt.
Over time, many attempts have been made to distribute abrasive grits on the backing in such a method that a higher percentage of the abrasive grits can be used. Merely depositing a thick layer of abrasive grits on the backing will not solve the problem, because grits lying below the topmost grits are not likely to be used. The use of agglomerates having random shapes where abrasive particles are bound together by means of a binder are difficult to predictably control the quantity of abrasive grits that come into contact with the surface of a workpiece. For this reason, the precisely shaped (pyramid) abrasive agglomerates are prepared. Some pyramid-shaped particles are formed which do not contain any abrasive particles and these are used as dilutants to act as spacers between the pyramid abrasive agglomerates when coated by conventional means. Many different fillers and additives can be used including talc and montmorillonite clays. Care is exercised to provide sufficient curing of the agglomerate binders in the drum cavities so that the geometry of the cavity is replicated. Generally, this requires a fairly slow rotation of the production tooling cavity drum. No description is given to the accuracy of the height or thickness control of the resultant abrasive article which incorporates these very large agglomerate pyramids which typically are 530 micrometers high and have a 530 micrometer base length. Thickness variations of conventional lapping disk abrasive sheets generally are held within 3 micrometers in order for it to be used successfully. The system of using the large pyramids described here cannot produce an abrasive article of the precise thickness control required for high speed lapping for a number of fundamental reasons. Some of these reasons are listed here. First, creation of many precise sized pyramid cavities by use of a belt that is replicated into a plastic form to control the belt cost adds error due to the sequential steps taken in the replication process. Variations in binder cures from production run to run and also variations in binder cures across the surface of a drum belt result in pyramids that are distorted from the original drum wells. For backing belts to be integrally bonded to the pyramids during the formation of the pyramids, it is required that any adhesive binder used to join the agglomerate be precisely controlled in thickness. Thickness control is difficult to achieve with this type of production equipment as there are many thickness process variables that must be controlled that are in addition to those variables that are controlled to successfully create or form precise shaped pyramids. The backing material must be of a precise thickness. Random orientation of the large agglomerates will inherently produce different heights at the exposed tops of the agglomerates depending on whether an agglomerate has its apex up, it lays sideways, or has its sharp apex embedded in a make coat of binder. The use of pyramids where all the apexes are up and the bases are nested close together produces grinding effects that change drastically from the initial use where only the tips of the pyramids contact the workpiece, to a final situation where the broad bases contact the workpiece when most of the pyramid has worn away. There was no description of the inherent advantage of the use of upright pyramids for hydroplaning or swarf removal which is a natural affect of these relatively tall “mountain pyramids” and the “valleys” between them which can carry off the water quite well. There was no discussion of the use of this pyramid material for high speed lapping or grinding. The water lubricant effects on grinding would change significantly as the abrasive article wears down. There is a fundamental flaw in the design of the pyramid for upright use. Most of the abrasive material contained on the pyramid lies at the base which is worn out last during the phase of wear when the variations in thickness of the backing, and other thickness variation sources, prevent a good proportion of the bases from contacting a workpiece surface. When using these large-sized pyramid agglomerates, they are designed to progressively breakdown and expose new cutting edges as the old worn individual abrasive particles are expended as the support binder is worn down, exposing fresh new sharp abrasive particles. Most of the value of the expensive abrasive particles lies in the base, as most of the volume of a triangle is in the base. Here, most of the valuable abrasive particles at the base areas will never be used and are wasted. Further, as wear-down of the pyramids is prescribed by selection of the pyramid agglomerate binder, the level surface of the abrasive disk will vary from the inside radius to the outside radius as the contact surface speed with a workpiece will be different due to the radius affect of a rotating abrasive platen. The pyramids are grossly high compared to the size of abrasive particles or abrasive agglomerates and this height results in uneven wear across the surface of an abrasive article that often is far in excess of that allowable for high speed flat lapping. This uneven wear prevents the use of this type of article for high speed lapping. Inexpensive abrasive materials such as aluminum oxide can be used for the pyramid agglomerates but it is totally impractical to use the extra hard, but very expensive, diamond abrasives in these agglomerates. The flaws inherent in the use of conventional pyramid shaped type of agglomerates, due to the size variations in the agglomerates, would tend to prevent them from being used successfully for flat lapping. First, agglomerates can be made and then sorted by size prior to use as a coated abrasive. Also, the configuration of a generally round shaped conventional agglomerate would certainly wear more uniformly than wearing down a pyramid which has a very narrow spiked top and, after wear-down, a base which is probably ten times more large in cross-sectional surface area than the pyramid top. Random orientation of the pyramid shape does not help this geometric artifact. Another issue is the formulation of the binder and filling used in a conventional agglomerate. A wide range of friable materials such as wood products can be joined in a binder which can be selected to produce an agglomerate by many methods, including furnace baking, etc. The binder used in the production of the pyramids must be primarily selected for process compatibility with the fast cure replication of the drum wells and not for consideration of whether this binder will break down at the desired rate to expose new abrasives at the same rate the abrasive particles themselves are wearing down. It does not appear that this pyramid shaped agglomerate particle has much use for high speed lapping. Use of a polyethylene terephthalete polyester film with a acrylic acid prime coat is described.
U.S. Pat. No. 4,652,275 (Bloecher) describes the use of erodible agglomerates of abrasive particles used for coated abrasive articles. The matrix material, joined together with the abrasive particles, erodes away during grinding which allows sloughing off of spent abrasive particles and the exposure of new abrasive grains. The matrix material is generally a wood product such as wood flour selected from pulp. A binder can include a variety of materials including phenolics. It is important that the binder not soften due to heat generated by grinding action. Instead, it should be brittle so as to breakaway. If too much binder is used, the agglomerate will not erode and if too little is used, the mixture of the matrix and the abrasive particles are hard to mix. The preferred agglomerate is made by coating a layer of the mixture, curing it, breaking it into pieces and separating the agglomerate particles by size for coating use. Agglomerates of a uniform size can be made in a pelletizer by spraying or dropping resin into a mill containing the abrasive mineral/matrix mixture. Agglomerates are typically irregular in shape, but they can be formed into spheres, spheroids, ellipsoids, pellets, rods and other conventional shapes. Other methods of making agglomerates include the creation of hollow shells of abrasive particles where the shell breaks down with grinding use to continually expose new abrasive particles. Other solid agglomerates of abrasive particles are mixed with an inorganic, brittle cryolite matrix. A description is made of conventional coated abrasives which typically consist of a single layer of abrasive grain adhered to a backing. It has been found that only up to 15 percent of the grains in the layer are actually utilized in removing any of the workpiece. It follows then that about 85 percent of the grains in the layer are wasted. The agglomerates described here preferably range from 150 micrometers to 3000 micrometers and have between 10 and 1000 individual abrasive grain particles for P180 grains and only 2 to 20 grains of larger P36 grains. These agglomerates far exceed the size required for high speed lapping. In fact, only single layers of diamond particles is required or typically used as a coating for most lapping abrasive articles, so these huge agglomerates have little or no use in lapping. Further, there would not be an effective method of maintaining a flat abrasive surface as the abrasive agglomerates are worn down by abrasive lapping or grinding action.
U.S. Pat. No. 4,799,939 (Bloecher) describes use of 70 micrometer diameter hollow glass spheres which are mixed with abrasive particles and a binder to form erodible 150 to 3000 micrometer agglomerates which are used for coating in abrasive articles. The hollow glass spheres are strong enough for the mixing operation and for the process used to form the agglomerate particle. However, they are weak enough that they break when used in grinding. Again, as for U.S. Pat. No. 4,652,275, these agglomerates are much too large and inappropriate for use in high speed lapping.
U.S. Pat. No. 4,327,156 (Dillon) describes a plastic mold cavity made from a powdered metal binder mixture that was molded in a RTV rubber mold. An A-6 tool steel powder is mixed with a thermosetting adhesive binder that is diluted with a liquid that is a good solvent for the uncured binder but poor solvent for the cured binder. This diluent/thermoset binder can be mixed with powdered metals, deposited in a mold, solidified by curing and the form shape can be fired in a furnace to produce an exact replica of the original mold shape that is a few percent smaller than the original shape. The diluent comes out of phase with the thermoset binder and is exhausted from the green powder shape, leaving the thermoset binder attaching each powdered metal particle bound to adjacent particles. Furnace heating is continued at a higher temperature and a porous metal shape is created which can be filled with molten copper by wicking action. Here, a completely solid metal form has been produced which is an extremely accurate representation of the original shape. This same technology can be used to form island base foundations of raised abrasive islands.
These systems have been described as providing benefits to particular technical and commercial fields, but they have not been shown to provide any particular benefits to truly high speed lapping/polishing systems and materials. No operational speeds are listed in any of the reference patents listed here indicates a lack of interest or awareness of the resultant artifacts of high speed lapping or polishing.
U.S. Pat. No. 794,495 (Gorton) discloses dots of abrasive on round disks formed by depositing abrasive particles on adhesive binder wetted dot areas printed on the backing, primarily to aid the free passage of grinding debris away from the workpiece surface. These dot areas are not elevated as raised island shapes from the surface of the backing.
U.S. Pat. No. 3,916,584 (Howard, et al.) discloses the encapsulation of 0.5 micron up to 25 micron diamond particle grains and other abrasive material particles in spherical erodible metal oxide composite agglomerates ranging in size from 10 to 200 microns and more. The large agglomerates do not become embedded in an abrasive article carrier backing film substrate surface as do small abrasive grain particles. In all cases, the composite bead is at least twice the size of the abrasive particles. Abrasive composite beads normally contain about 6 to 65% by volume of abrasive grains, and compositions having more than 65% abrasive particles are considered to generally have insufficient matrix material to form a strong acceptable abrasive composite granule. Abrasive composite granules containing less than 6% abrasive grains lack enough abrasive grain particles for good abrasiveness. Abrasive composite bead granules containing about 15 to 50% by volume of abrasive grain particles are preferred since they provide a good combination of abrading efficiency with reasonable cost. In the invention, hard abrasive particle grains are distributed uniformly throughout a matrix of softer microporous metal oxide (e.g., silica, alumina, titania, zirconia, zirconia-silica, magnesia, alumina-silica, alumina and boria, or boria) or mixtures thereof including alumina-boria-silica or others. Silica and boria are considered as metal oxides. The spherical composite abrasive beads are produced by mixing abrasive particles into an aqueous colloidal sol or solution of a metal oxide (or oxide precursor) and water and the resultant slurry is added to an agitated dehydrating liquid including partially water-miscible alcohols or 2-ethyl-1-hexanol or other alcohols or mixtures thereof or heated mineral oil, heated silicone oil or heated peanut oil. The slurry forms beadlike masses in the agitated drying liquid. Water is removed from the dispersed slurry and surface tension draws the slurry into spheroidal composites to form green composite abrasive granules. The green granules will vary in size; a faster stirring of the drying liquid giving smaller granules and vice versa. The resulting gelled green abrasive composite granule is in a “green” or unfired gel form. The dehydrated green composite generally comprises a metal oxide or metal oxide precursor, volatile solvent, e.g., water, alcohol, or other fugitives and about 40 to 80 weight percent equivalent solids, including both matrix and abrasive, and the solidified composites are dry in the sense that they do not stick to one another and will retain their shape. The green granules are thereafter filtered out, dried and fired at high temperatures. The firing temperatures are sufficiently high, at 600 degrees C. or less, to remove the balance of water, organic material or other fugitives from the green composites, and to calcine the agglomerate body matrix material to a firm, continuous, microporous state (the matrix material is sintered), but insufficiently high to cause vitrification or fusion of the agglomerate interior into a continuous glassy state. These abrasive composite agglomerate beads incorporate abrasive particles 25 microns and less sized particles, as abrasive particle grains 25 microns and larger can be coated on abrasive articles to form useful materials. In one example, a slurry of the average sized 50 micron abrasive agglomerates was mixed in a phenolic resin and was knife coated with a 3 mil (0.003 inch or 72 micron) knife gap setting which exceeded the size of the agglomerates. As the individual abrasive particles were smaller than the depth of the coated resin binder slurry, there is indication that enough resin binder solvent was evaporated after coating to expose a substantial portion of the individual coated abrasive agglomerates when the abrasive product was dried. U.S. Pat. No. 3,916,584 (Howard, et al.) is herein incorporated by reference.
U.S. Pat. No. 5,232,470 (Wiand) discloses raised molded protrusions of circular shapes composed of abrasive particles mixed in a thermoplastic binder attached to a circular sheet of backing.
U.S. Pat. No. 5,910,471 (Christianson, et al.) discloses that the valleys between the raised adjacent abrasive composite truncated pyramids provide a means to allow fluid medium to flow freely between the abrasive composites which contributes to better cut rates and the increased flatness of the abraded workpiece surface.
U.S. Pat. No. 6,186,866 (Gagliardi) discloses the use of a abrasive article backing contoured by grinding-aid containing protrusions having a variety of peak-and-valley shapes. Abrasive particles are coated on both the contoured surfaces of the protrusions and also onto the valley areas that exist between the protrusion apexes. The protrusions present grinding aid to the working surface of the abrasive article throughout the normal useful life of the abrasive article. Useful life of an abrasive article begins after the abrasive particle coating that exists on the protrusion peaks is removed, which typically occurs within the first several seconds of use. Initial use, which occurs prior to the “useful life”, is defined as the first 10% of the life of the abrasive article. Protrusions contain a grinding aid, with the protrusions preferably formed from grinding aid alone, or the protrusions are a combination of grinding aid and a binder. The protrusion shapes have an apex shape that is coated with an adhesive resin and abrasive particles. The particles are drop coated or electrostatically coated onto the resin and thereby form a layer of abrasive particles conformably coated over both the peaks and valleys of the protrusion shapes. The primary objective of the protrusion shapes is to continually supply a source of grinding aid to the abrading process. There are apparent disadvantages of this product. Only a very few abrasive particles reside on the upper-most portions of the protrusion peaks and it is only these highest-positioned particles that contact a workpiece surface. The small quantity of individual particles contacting a workpiece, which are only a fraction of the total number of particles coated on the surface of the abrasive article, will be quickly worn down or become dislodged from the protrusion peaks. Particles would tend to break off from the protrusion wall surfaces, when subjected to abrading contact forces, due to the inherently weak resin particle bond support at individual particle locations on the curved protrusion walls. Abrasive particles are very weakly attached to the sloping sidewalls of the protrusions due to simple geometric considerations that make them vulnerable to detachment. It is difficult to bond a separate abrasive particle to a wall-side with a resin adhesive binder that does not naturally flow by gravity and symmetrically surrounds the portion of the particle that contacts the wall surface. Abrasive particles attached to a traditional flat-surfaced abrasive backing sheet article tend to have a symmetrical meniscus of resin surrounding the base of each particle but this configuration of meniscus would not generally form around a particle attached to a near vertical protrusion side-wall. Also, the protrusion side-wall is inherently weak as the protrusion body is constructed of grinding aid material. Much of the valuable superabrasive particles located in the valley areas are not utilized with this technique of particle surface conformal coating of both protrusion peaks and valleys. As the abrading action continues, with the wearing down of the erodible protrusions, more abrasive particles are available for abrading contact with a workpiece article. However, the advantage of having protrusion valleys, that are used to channel coolant fluids and swarf, disappears as the valleys cease to exist. The procedure cited for testing the protrusion contoured abrasive article cited the use of a 7 inch (17.8 cm) diameter disk operated at approximately 5,500 rpm indicating an intended high surface speed abrading operation.
U.S. Pat. No. 6,231,629 (Christianson, et al.) discloses a slurry of abrasive particles mixed in a binder and applied to a backing sheet to form truncated pyramids and rounded dome shapes of the resin based abrasive particle mixture. Fluids including water, an organic lubricant, a detergent, a coolant or combinations thereof are used in abrading which results in a finer finish on glass. Fluid flow in valleys between the pyramid tops tends to produce a better cut rate, surface finish and increased flatness during glass polishing. Presumably, these performance advantages would last until the raised composite pyramids or domes are worn away. Abrasive diamond particles may either have a blocky shape or a needle like shape and may contain a surface coating of nickel, aluminum, copper, silica or an organic coating.
U.S. Pat. No. 6,217,413 (Christianson) discloses the use of phenolic or other resins where abrasive agglomerates are drop coated preferably into a monolayer. Leveling and truing out the abrading surface is performed on the abrasive article which results in a tighter tolerance during abrading.
U.S. Pat. No. 6,299,508 (Gagliardi, et al.) discloses abrasive particle coated protrusions attached to a backing sheet where the protrusions have stem web or mushroom shapes with large aspect ratios of the mushroom shape stem top surface to the stem height. A large number of abrasive particles are attached to the vertical walls of the stems compared to the number of particles attached to the stem top surface. Abrasive discs using this technology range in diameter from 50 mm (1.97 inches) to 1,000 mm (39.73 inches) and operate up to 20,000 revolutions per minute. As in Gagliardi, U.S. Pat. No. 6,186,866, the abrasive article described here does not provide that the attachment positions of the individual abrasive particles are in a flat plane which is required to create an abrasive article that can be used effectively for high surface speed lapping.
U.S. Pat. No. 6,319,108 (Adefris, et al.) discloses the electroplating of composite porous ceramic abrasive composites on metal circular disks having localized island area patterns of abrasive composites that are directly attached to the flat surface of the disk
U.S. Pat. No. 6,371,842 (Romero) describes abrasive grinding disk articles that have an article center aperture hole and circular bands of raised islands having flat top surfaces that are adhesive coated and abrasive particles which are deposited onto the adhesive. The abrasive articles described are not suggested for nor is awareness indicated for their use in flat lapping or in flat grinding where the disks would be mounted on a flat surfaced rotary platen. Instead the articles are taught to be mounted on hand tool mandrels by the use of mechanical fasteners that penetrate an aperture hole located at the center of the circular disk. No mention or teachings are made of the art of precision flat grinding, or lapping, of flat workpiece surfaces or of using these island disks in that abrasive application area. Also, there is no mention of the precision control of the variation in the thickness of the abrasive disk articles or the use of the precision flatness grinding or lapping machines that are required to produce precise flat workpiece surfaces. There is no mention of the desirability of the existence of a mono (single) layer of coated abrasive particles; or of controlling the variation of the thickness of the abrasive article to a proportion of the diameter of the coated abrasive particles. Further, no mention is made of the problems of hydroplaning of disks or workpieces. Instead, the raised island abrasive hand tool disks taught by Romero are intended to correct a specific problem that occurs in typical non-island disk manufacturing where thick preformed disks are coated with a adhesive binder that has a tendency to form a high lip of binder coating on the disk backing outer peripheral edge after which abrasive particles are deposited on the binder raised peripheral lip. This raised elevation outer diameter raised lip that is coated with abrasive particles causes undesirable workpiece surface scratches during abrading use. The use of abrasive coated raised island structures that are attached to a backing sheet reduces the formation of the raised abrasive peripheral edge lips on manual tool grinding disk articles.
Romero does not teach the advantages or requirements of having the features of uniform flat surfaces or even “substantially planar surfaces” for: the valley areas located between the islands; the top surfaces of the islands; or the back side surface of the backing in the non-claims portion of the patent specification. There is no reference given for the use of the island type abrasive articles to be used for creating precision flat workpiece surfaces or precise smooth workpiece surfaces as in a flat-lapping operation. Flat lapping requires extremely flat abrasive disk machine tool platens and the abrasive disk article also must be precisely flat and of uniform thickness to enable all of the coated abrasive particles to be utilized. Further, there is no mention of the advantages of arranging the raised islands in an annular array having a narrow outer radius annular band width of abrasive to avoid having the slow moving abrasive surfaces that are located at the inner diameter area of a disk, to be in contact with a workpiece surface. Uneven wear occurs across the surface of a workpiece when the workpiece is in contact with an abrasive article abrading surface that has both fast and slow surface speeds.
His abrasive disks have significant amounts of fibers and other fillers imbedded in the disk backing which tends to produce a disk of limited thickness uniformity. The preferred embodiment of Romeo is a thick fiber filled disk having integral raised islands that is constructed by: molding a flat disk with integral raised islands; or adhesively bonding island shapes cut out from sheet material to a backing disk; or embossing island shapes into the surface of a flat backing disk sheet. None of these three raised island disk manufacturing techniques would be expected to produce islands having precisely flat surfaces where the island height variations, as measured from the backside of the backing, is within the 0.0001 to 0.0003 inch (0.003 to 0.008 mm) tolerance that is typically required for 8,000 or more SFPM high speed platen flat lapping. The Romero disks are intended for use with manual grinding tools where the amount of workpiece material removal is of primary concern, rather than controlling the flatness of the workpiece. This type of grinding disk generally would have large sized abrasive particles that are not suitable for polishing or lapping operations. The described abrasive disk is frictionally mounted to a flexible backup pad that is attached to a mandrel with a disk-center screw-cap that penetrates the disk-center aperture hole and squeezes the disk against the flexible and conformable metal or polymer backup pad. The screw-cap mounting forces result in significant and uneven distortions of both the abrasive disk sheet and the backup pad prior to the moving abrasive contacting a workpiece. Romero does not teach the use of a circular disk backing that does not have a center hole aperture in the non-claims portion of the patent specification. He describes raised island abrasive substrate sheets having rectangle, square, hexagon, octagon and oval shapes. However, these non-circular shapes are intended to also be used with sheet center aperture holes, the same as for circular disks, to allow multiple layers of these non-circular abrasive sheets to be mounted on a mandrel. He incorporates by reference U.S. Pat. No. 5,142,829 (Germain) which describes a variety of these same types of non-circular abrasive sheet shapes, all having center aperture holes, where the holes allow them to be progressively stacked on a mandrel for use as a flapper abrasive portable manual tool. There is no mention of flat sheets, long strips or belts of abrasive coated raised island articles that do not have a disk-center aperture hole or where these disks would be used for non-manual tool abrading purposes. The only described disk articles are those that have disk-center aperture holes that are used exclusively on portable tool mandrels. The method described by Romero for coating the abrasive disk with abrasive particles is to first coat the island top surfaces with a make coat of binder, deposit loose abrasive particles on the make coat and then add a size coat of binder after which the binders are cured. Coating the island top surfaces with a abrasive slurry is not taught.
Romero does not teach the hydroplaning of workpieces surfaces when lapping at very high surface speeds. Hydroplaning would not be an issue when using a abrasive disk on a mandrel tool device as the abrasive article would have a line-shaped area of contact with a workpiece surface due to the abrasive article out-of-plane distortion by the tool operator. A water boundary layer does not build up in thickness and create hydroplaning for line-contact abrading surfaces because there is not enough distance for the water film to increase in thickness across the short distance of the line width. Also, there is a very high localized area of contact pressure at the abrading contact line area due to the large applied pressure that is distributed over a very small area. This high contact line-area pressure tends to prevent the boundary layer thickness buildup of coolant water. In the instance of flat lapping, the abrasive contacts the workpiece with a very low contact force across a full surface area that is typically as wide as the width of the workpiece. Due to the low contact force and large contact area, the water boundary layer can build up in substantial thickness across the relatively long distance that extends across the full length of the mutual abrading contact area. In this way, hydroplaning, where a portion of the workpiece is lifted from the abrasive surface by the depth or thickness of the water boundary layer, does not tend to occur for mandrel-and-pad type of manual tool abrading but is difficult to avoid for machine tool flat lapping.
Island types of abrasive articles used for precision flat grinding or lapping are primarily suited for use with rotating flat platen surfaces. The localized individual island sites are structurally stiff due to their increased thickness as compared to the thickness of the adjacent thin backing sheet. The flexural stiffness of the island areas is a function of the total island material thickness cubed, which means a relatively small change in the backing sheet material thickness at the location of a raised elevation island can change the localized stiffness of the island area by a very large amount. These abrasive coated stiff islands will not easily conform to a curved surface. Stiff raised large diameter islands that have a thin flat top surface coating of abrasive material will only be contacted by a workpiece at the central portion of the island abrasive when contacting a convex workpiece. Only the abrasive outer island peripheral edges of a stiff island would be contacted for a concave workpiece. In either case, abrading action results in uneven wear of both the island coated abrasive and of the workpiece surface. In a like manner, raised island abrasive disk articles having stiff islands that have their flat disk-plane surface distorted by manual pressure when contacting a flat workpiece will only be effective in uniform material removal if the island dimensions are very small, in particularly the tangential direction. Here, small islands can lay flat to a workpiece but only if the adjacent disk backing material that is located next to the islands is flexible enough to allow the island to bend enough to compensate for the disk out-of-plane distortion created by the abrasive tool operator. Even if the backing is flexible, the backing pad would tend to prevent this conforming action. Stiff and thick backings are generally used with manual abrasive disk articles as thin backings are too fragile for this type of abrading usage. Manual pressure will distort the disk plane in both a radial and tangential direction. This abrasive sheet distortion would prevent the production of a precision flat workpiece surface with this manual apparatus and abrasive article. Flexible sheets of a non-island uniform coated abrasive article having a thin backing will conform to a flat rigid platen which provides a natural flat abrading surface for the whole surface of the abrasive sheet. Likewise, a thin backing sheet or disk having integral raised islands will likewise conform to the flat platen surface where each of the individual islands will be presented with a flat island top surface that is mutually flat to the workpiece surface. Flexible abrasive sheets or disks having raised islands mounted on flat platens can be used effectively for the flat grinding and smooth lapping of a flat workpiece surfaces. The Romero described abrasive disks as used with conformable screw-cap mandrel pads are not practical for use for precision flat grinding. Conformable pad mandrels are generally used on portable grinding tools that are held with large (6 kilogram or 13 lbs) manual contact forces against a workpiece which deforms the flexible abrasive disk supporting pad to allow an area of the thick and stiff abrasive disk to be in flat contact with a workpiece surface. The whole large contact force tends to be concentrated at the typical small line-type contact area that exists between the abrasive and the workpiece surfaces. The manual abrasive grinding operator typically moves the disk with a random oscillation-type orientation motion relative to the surface of the workpiece. In the comparative case of a flat lapping machine, a low contact force of 1 to 2 lbs (0.5 to 1 kg) is spread evenly over large surface areas of a workpiece that is supported by a workpiece holder spindle. The workpiece spindle of a flat lapping machine is typically orientated perpendicular to the surface of an abrasive disk that is flat mounted to a rigid platen. A manual abrasive disk tool is typically oriented at a significant angle to the workpiece surface. Very low stresses are induced within the thin and weak abrasive backing sheet used in flat lapping because the relatively large mutual flat workpiece and abrasive contact surface areas do not create localized areas of abrading contact forces. Thin backings as used with the manual tool grinding pad disks is stated by Romero to be a problem as this fragile type of disk easily rips and tears and can crease and pucker the disk article.
U.S. Pat. No. 5,733,175 (Leach) describes workpiece polishing machines with overlapping platens that provide uniform abrading velocities across the surface of the workpiece. Hydroplaning of workpieces during abrading action is discussed.
U.S. Pat. No. 4,586,292 (Carroll et al.) describes an apparatus that provides a complex rotary motion used to lap polish the inside diameter of a spherical surface workpiece.
U.S. Pat No. 3,702,043 (Welbourn et al.) describes a machine used for removing material from the internal surface of a workpiece and the use of a strain gage sensor device that indicates the cutting force exerted by the cutting tool upon the workpiece.
U.S. Pat. No. 5,190,568 (Tselesin) discloses a variety of sinusoidal and other shaped peak and valley shaped carriers that are surface coated with diamond particles to provide passageways for the removal of grinding debris. There are a number of problems inherent with this technique of forming undulating row shapes having wavelike curves that are surface coated with abrasive particles on the changing curvature of the rows. The row peaks appear to have a very substantial heights relative to the size of the particles which indicates that only a very small percentage of the particles are in simultaneous contact with a workpiece surface. One is the change in the localized grinding pressure imposed on individual particles, in newtons per square centimeter, during the abrading wear down of the rows. At first, the unit particle pressure is highest when a workpiece first contacts only the few abrasive particles located on the top narrow surface of the row peaks. There is a greatly reduced particle unit pressure when the row peaks are worn down and substantially more abrasive particles located on the more gently sloped side walls are in contact with the workpiece. The inherent bonding weakness of abrasive particles attached to the sloping sidewalls is disclosed as is the intention for some of the lower abrasive particles, located away from the peaks, being used to structurally support the naturally weakly bonded upper particles. The material used to form the peaks is weaker or more erodible than the abrasive particles, which allows the erodible peaks to wear down, expose, and bring the work piece into contact with new abrasive particles. Uneven wear-down of the abrasive article will reduce its capability to produce precise flat surfaces on the work piece. Abrasive articles with these patterns of shallow sinusoidal shaped rounded island-like foundation ridge shapes where the ridges are formed of filler materials, with abrasive particles coated conformably to both the ridge peaks and valleys alike is described. However, the shallow ridge valleys are not necessarily oriented to provide radial direction water conduits for flushing grinding debris away from the work piece surface on a circular disk article even prior to wear-down of the ridges. Also, a substantial portion of the abrasive particles residing on the ridge valley floors remain unused as it is not practical to wear away the full height of the rounded ridges to contact these lower elevation particles.
U.S. Pat. No. 4,930,266 (Calhoun, et al.) discloses the application of spherical abrasive composite agglomerates made up of fine abrasive particles in a binder in controlled dot patterns where preferably one abrasive agglomerate is deposited per target dot by use of a commercially available printing plate. Small dots of silicone rubber are created by exposing light through a half-tone screen to a photosensitive silicone rubber material coated on an aluminum sheet and the unexposed rubber is brushed off leaving small islands of silicone rubber on the aluminum. The printing plate is moved through a mechanical vibrated fluidized bed of abrasive agglomerates which are attracted to and weakly bound to the silicone rubber islands only. The plate is brought into nip-roll pressure contact with a web backing which is uniformly coated by a binder resin which was softened into a tacky state by heat thereby transferring each abrasive agglomerate particle to the web backing. Additional heat is applied to melt the binder adhesive forming a meniscus around each particle, which increases the bond strength between the particle and the backing. The resulting abrasive article has gap-spaced dots of abrasive agglomerate particles on the backing but the agglomerates are attached directly to the backing surface and are not raised away from the backing surface. Each composite abrasive agglomerate preferably is a spherical composite of a large number of abrasive grains in a binder; the agglomerates typically range in size from 25 to 100 microns and contain 4-micron abrasive particles. It is indicated that the composite abrasive agglomerate granules should be of substantially equal size, i.e., the average dimension of 90% of the composite granules should differ by less than 2:1. Abrasive grains having an average dimension of about 4 microns can be bonded together to form composite sphere granules of virtually identical diameters, preferably within a range of 25 to 100 microns. Preferably, the abrasive composite granules have equal sized diameters where substantially every granule is within 10% of the arithmetic mean diameter so that the granules protrude from the surface of the binder layer to substantially the same extent and also so the granules can be force-loaded equally upon contacting a workpiece. Granules are spherical in shape or have a shape that has approximately that same thickness in every direction. By individually positioning the equal sized granules to be spaced equally from adjacent granules, the granules each bear the same load and hence wear at substantially identical rates and tend to be equally effective. Consequently, workpieces continue to be polished uniformly. One difficulty with this abrasive product, even with abrasive composites having uniform diameters where each composite granule can be positioned to protrude to the same extent from the binder layer, the variation in the thickness in the backing thickness is not considered. If there are significant variations in the backing thickness, even equal sized individual composite abrasive agglomerates coated on a abrasive article rotating at high lapping surface speeds of 8,000 surface feet per minute will not evenly contact a workpiece surface. Eventually, the highest positioned composite abrasives will wear down and adjacent composite agglomerates will be contacted by the workpiece surface. It is necessary to control the diameter of the composite agglomerates, the thickness variation of the binder and the variation of the coated surface height of the backing, relative to the back platen mounting side of the backing, to some fraction of the diameter of the average diameter of the abrasive composites to attain effective utilization of all or most of the abrasive composite agglomerates.
U.S. Pat. No. 5,251,802 (Bruxvoort, et al.) discloses the use of solder or brazing alloys to bond diamond and other abrasive particles to a flexible metal or non-metal backing material.
U.S. Pat. No. 5,496,386 (Broberg, et al.) discloses the application of a mixture of diluent particles and also shaped abrasive particles onto a make coat of resin where the function of the diluent particles is to provide structural support for the shaped abrasive particles.
Abrasive tools having an annular band of raised islands containing diamond particles impregnated in a metal matrix have been available from the Boart Longyear Interfels of Bad Bentheim, Germany for use in rock core drilling. These toolbits have a inside annular band diameter that is approximately 60% of the annular band outside diameter. They have a similar construction appearance to the flexible sheet abrasive articles having an annular band of raised islands that are described here.